Abstract: An apparatus for ion-implantation in elements, especially discs of semi-conducting material, in which a vacuum container has an end wall which has lock means by which the elements may be passed from the outside of the container to a position in the end wall, where one of its surfaces is exposed to the vacuum space in the container and treated by ions. The lock means includes a rotatable slide valve mounted between two parallel walls in one of which an aperture to the outer atmosphere is provided and in the second of which an aperture to the inner space of the container is provided. A number of apertures, corresponding to the said apertures in the walls, are provided in the slide value. The elements are positioned in one of the apertures in the slide valve, and by its rotation, conveyed to the wall aperture opening into the vacuum space. In the two parallel walls, two sets of cavities are provided, one encircling the other, each of which is connected to a separate vacuum source.